1. Field of the Invention
This invention relates to improvements in an etching apparatus utilizing a microwave discharge plasma, and more particularly, to an enhancement in the etching performance as well as an improvement in the processing capability of the etching apparatus.
2. Description of the Prior Art
In recent years, in the field of surface processing of semiconductors and metals, the conventional wet processing method has been extensively replaced by a dry processing method. As one type of apparatus suitable for the dry etching of a semiconductor surface, the inventors have previously developed an etching apparatus which uses a microwave discharge plasma for the etching operation, as disclosed in Japanese Patent Application Publication No. 44795/1978.
This microwave plasma etching apparatus is constructed such that the surface of a sample is exposed to the plasma produced by a microwave discharge, so as to etch and process the sample surface. This technique has the advantage that a fine etching is possible with the chance of damage to the sample lessened. On the other hand, however, if the etching of the sample surface is performed under conditions in which a single sample, or a small number of samples, is inserted and fixed in a plasma exposure region in the conventional manner, a problem will occur with respect to the processing capability. Moreover, it is feared that the continuous exposure of the sample to the plasma for too long a time will raise the temperature of the sample excessively, resulting in various drawbacks, such as the changing of the quality of the photoresist mask overlying the sample surface.
As an expedient for solving these problems, there has been proposed an apparatus wherein a plurality of samples are placed on a turntable and wherein, as the turntable rotates, the plurality of samples pass through a plasma exposure region in succession, as disclosed in Japanese Patent Application Publication No. 34463/1978. According to this method, it becomes possible to etch and process the plurality of samples simultaneously, so that the processing capability of the apparatus is markedly enhanced. In addition, since the individual samples are alternately subjected to heating and cooling periodically, an excessive temperature rise in the samples is avoided.
With this method, however, since the samples are transported within the plasma exposure region, which provides a substantially-uniform plasma density, while revolving along a circular path, the etching speed on the surface of each sample differs depending upon the distance of the point on the sample from the center of revolution thereof, resulting in the difficulty that a uniform etching of the sample cannot be obtained over the whole sample surface. In other words, since the points on the sample will be moving at different speeds depending on their distance from the center of the turntable, each point will be in the plasma exposure region for a different length of time, causing a variation in the degree of etching across the surface of the sample.